Cell Signaling Principles and Pathways

These vocabulary flashcards cover fundamental cell signaling principles, various forms of intercellular communication, receptor classes (GPCR, ICCR, ECR), and specific intracellular pathways such as cAMP, Calcium, and RTK/MAP kinase cascades.

Ligand

An extracellular signal molecule that binds to a receptor protein on the plasma membrane to activate intracellular signaling molecules.

Effector proteins

Proteins that mediate cell response through signal amplification; examples include metabolic enzymes, transcription regulatory proteins, and cytoskeletal proteins.

Autocrine signaling

A form of intercellular signaling where a cell targets itself, such as the EL1 cytokine produced by monocytes.

Contact-dependent signaling

Signaling where a ligand is exposed on the surface of a neighboring cell, such as muscle cells sending $Ca^{2+}$ through gap junctions.

Paracrine signaling

Signaling where one cell secretes a signaling molecule that acts on nearby neighbors, such as estrogen from ovaries affecting ovarian follicle maturation.

Endocrine signaling

Signaling where a hormone is released from a cell and travels long distances to act on a target cell, such as thyroid hormone from the thyroid gland.

Bacterial quorum sensing

A process that uses cell density to turn gene transcription on or off; specifically studied in Vibrio chlorae.

LuxI (autoinducer synthase)

A small molecule synthesized and released by Vibrio chlorae; increased levels during high cell density activate virulent gene expression.

LuxR receptor

A receptor in Vibrio chlorae that remains inactive at low cell density but binds to LuxI at high density to activate luciferase genes.

Intracellular receptors

Receptors that bind small, hydrophobic signaling molecules, such as steroids, which traverse the cell membrane.

Cell-surface receptors

Receptors that bind hydrophilic signal molecules via high-affinity, non-covalent interactions involving polar or charged amino acids.

Fast cellular response

Responses involving altered protein function, such as metabolic enzymes, cell shape changes, or ion channel movements, occurring in less than 1 second to minutes.

Slow cellular response

Responses involving altered protein synthesis via gene expression, typically taking minutes to hours.

GPCR (G-protein coupled receptor)

A cell-surface receptor characterized by 7 TM alpha helices that undergoes conformational changes to affect G proteins.

ICCR (ion-channel coupled receptor)

A major class of cell-surface receptors often involved in vision and olfaction systems.

ECR (enzyme-coupled receptor)

A major class of cell-surface receptors that convert extracellular information into intracellular signals by acting as or activating enzymes.

Protein Kinases

Proteins that turn a signal 'on' by phosphorylating a target using ATP; eukaryotes use serine/threonine or tyrosine, while bacteria use histidine.

Protein Phosphatase

An enzyme that turns a protein 'off' by removing a phosphate group.

GEF (Guanine exchange factor)

A protein that activates G proteins by exchanging bound GDP for GTP.

GAP (GTPase activating protein)

A protein that performs GTP hydrolysis to convert bound GTP back to GDP, turning the protein 'off'.

Heterotrimeric G protein

A protein complex consisting of alpha, beta, and gamma subunits that is activated by GPCRs.

Adenylyl cyclase

An enzyme activated by G proteins that converts ATP into cAMP, representing a fast intracellular pathway.

PKA (Protein Kinase A)

A kinase activated by cAMP that enters the nuclear pore to phosphorylate CREB.

CREB

A protein that, once phosphorylated by PKA, binds to the CRE (cAMP response element) promoter to activate gene transcription.

Phospholipase C-beta

An enzyme activated by a G protein that cleaves diacylglycerol from $IP_3$ (inositol triphosphate).

IP3 (inositol triphosphate)

A molecule that binds to and opens $IP_3$-gated $Ca^{2+}$-release channels in the ER lumen.

PKC (Protein Kinase C)

A kinase bound to diacylglycerol that is activated by $Ca^{2+}$ to regulate cell proliferation, differentiation, apoptosis, and migration.

Rhodopsin

A receptor in the vision system that, when activated by light, activates the G protein transducin.

Transducin

The specific G protein in the photoreceptor pathway activated by light-absorbed rhodopsin.

Cyclic GMP phosphodiesterase

An enzyme activated by transducin that hydrolyzes cyclic GMP to close cation channels, leading to cell hyperpolarization.

RTK (Receptor Tyrosine Kinase)

An enzyme-coupled receptor that dimerizes and phosphorylates its own tyrosine kinase domain upon ligand binding.

SH2 domain

A protein domain that allows downstream signaling proteins to bind to phosphorylated tyrosine ($Try-P$) sites on RTKs.

Ras protein

A small GTP-binding protein activated by Ras GEF downstream of RTKs; it initiates the MAP kinase cascade.

Mitogen

A small molecule that triggers mitosis.

Raf

Also known as MAP kinase kinase kinase; it is the first kinase in the MAP kinase cascade activated by GTP-bound Ras.

Mek

Also known as MAP kinase kinase; it is phosphorylated and activated by Raf.

Erk

Also known as MAP kinase; it is phosphorylated by Mek and leads to changes in protein activity or gene expression.